Wholly aromatic liquid crystalline polyester amide resins have rigid molecules, which may be present in a liquid crystalline state without entanglement between molecules even in a molten state, and exhibit the behavior of molecular chains being oriented in a flow direction of the wholly aromatic liquid crystalline polyester amide resin by shear force when being molded. Thus, wholly aromatic liquid crystalline polyester amide resins exhibit the behavior in which the melt viscosity thereof suddenly decreases even though small shear force is applied thereto or the melt viscosity thereof rapidly decreases as the temperature increases.
Due to having these characteristics, wholly aromatic liquid crystalline polyester amide resins have good flowability and resistance to heat, and thus, have been widely used as a material for vehicle parts, electric and electronic parts, and small and precise molded products.
Due to the recent remarkable industrial advances, the uses of wholly aromatic liquid crystalline polyester amide resins tend to become more sophisticated and specialized. In addition, wholly aromatic liquid crystalline polyester amide resins have good fluidity for efficient and economical injection molding. Such wholly aromatic liquid crystalline polyester amide resins are good, more specifically, in heat resistance, resistance to hydrolysis and dimensional stability at a high temperature, and mechanical strength, such as flexural strength, tensile strength, impact strength, and thus, have extended uses as materials for coil bobbins which need to solder at a high temperature, connectors for electric and electronic parts, relay, various vehicle parts, containers, films, and substrates.
Such wholly aromatic liquid crystalline polyester amide resins may be prepared by condensation polymerization between at least two different monomers.
Wholly aromatic liquid crystalline polyester amide resins may be prepared by acetylating a monomer having a hydroxyl group and a monomer having an amino group or acetylating a monomer having both a hydroxyl group and an amino group and then condensation-polymerizing the acetylated monomers with aromatic dicarboxylic acid. In this regard, the monomer having an amino group is necessarily used in the acetylating process.
The condensation polymerization reaction is conducted at a high temperature, and the monomer having an amino group is easy to be pyrolyzed at a high temperature or oxidized by oxygen in air and thus the pyrolysis or oxidation of the amino group needs to be prevented by acetylating the amino group before the condensation polymerization reaction. If the amino group is not completely acetylated in the acetylating of the monomer, however, remaining amino groups are pyrolyzed during the high-temperature condensation polymerization, thereby producing a gaseous byproduct and thus the surface of a reaction product foams, whereby the surface thereof swells. If the surface of the reaction product swells to an upper top of a reactor, a column for exhausting the gaseous byproduct may be clogged, thus not being able to remove the gaseous byproduct any longer. This may deteriorate physical properties of a wholly aromatic liquid crystalline polyester amide prepolymer and wholly aromatic liquid crystalline polyester amide resins, and further cause a processing hindrance, which requires disassembling and cleaning of the reactor. Indeed, when monomers having amino groups and monomers having hydroxyl groups are simultaneously acetylated, 80 to 90% of the amino groups are acetylated. On the other hand, when monomers having amino groups and monomers having hydroxyl groups are separately acetylated, 95 to 97% of the amino groups are acetylated. Since the amino groups are not completely acetylated in any case, problems due to byproducts such as a carbonyl compound (e.g., benzoquinone) may occur. Such problems will be described below.
In addition, if the gaseous byproduct is not removed from the reaction product during the condensation polymerization reaction even though the foaming caused by the gaseous product does not reach the upper top of the reactor, the resulting wholly aromatic liquid crystalline polyester amide resin may not have uniform physical properties. As a result, wholly aromatic liquid crystalline polyester amide resin compounds and molded products manufactured from the wholly aromatic liquid crystalline polyester amide resin may have non-uniform, poor physical properties. In particular, the aromatic polyester resin compound may have reduced mechanical strength, and the molded products may undergo blistering when left in high-temperature air or liquid for a long time.
In addition, when monomers having amino groups are reacted not in an inert gas atmosphere but in air atmosphere, the amino groups are oxidized by oxygen in air, thereby forming carbonyl groups. In other words, the monomers having amino groups are converted to carbonyl compounds (e.g., benzoquinone), which are susceptible to sublimation. Thus, the equilibrium between the equivalents of the monomers is destroyed during the condensation polymerization reaction and, as a result, the reaction is not smoothly performed. In addition, if the carbonyl compound is bound to a terminal portion of the formed resin by the condensation polymerization reaction, the condensation polymerization reaction is not performed on the terminal portion thereof any longer and thus the molecular weight of the formed resin does not further increase. Furthermore, a carbonyl compound such as benzoquinone changes a color of the formed resin into red and rapidly reduces the fluidity of the formed resin.